1. Field of the Invention
The present invention relates to a storage medium having stored therein an image display program for displaying an image using an augmented reality technique, an image display apparatus, an image display system, and an image display method.
2. Description of the Background Art
In the prior art, there are augmented reality techniques in which an image of the real space (image captured by a camera) and an image of a virtual space (CG image) are synthesized and displayed together. Non-Patent Document 1 (Hirokazu Kato, Mark Billinghurst, “Marker Tracking and HMD Calibration for a video-based Augmented Reality Conferencing System”, proceedings of IWAR99 (the 2nd International Workshop on Augmented Reality), the United States, October 1999) describes a basic image generating method of an augmented reality technique. In an augmented reality technique, markers are placed in the real space, and a camera is used to capture an image around a marker. The marker in the captured image is detected by an image recognition process, and the three-dimensional position of the marker is calculated. It is possible to display an image in which a virtual object is synthesized with the captured image of the real space by generating an image (CG image) of the object in the virtual space by using the calculated three-dimensional position, and displaying the generated image while synthesizing it at the position of the marker in the camera image.
With the conventional augmented reality technique, the real captured image and the virtual CG image may be displayed with misalignment or the CG image may be displayed with flickering.
In an augmented reality technique, it is necessary to calculate the three-dimensional position of a marker by recognizing the marker included in the captured image, and such recognition and calculation processes are time-consuming. Therefore, the CG image generated based on the recognition and calculation process results lags behind the captured image in time. Therefore, when the camera is moved and the captured image changes, a CG image to be synthesized with the captured image lags behind in time and is therefore synthesized at a position before the change, thus resulting in misalignment between the position of the marker in the captured image and the position at which the CG image is synthesized.
In practice, even if a marker is captured, the recognition process may fail by failing to successfully recognize the marker from the captured image. If the recognition process fails, a CG image cannot be generated from the captured image which is the subject of the recognition process, and thus only the captured image is displayed. Therefore, if the recognition process fails intermittently, the CG image is displayed with flickering.
As described above, in the prior art, a CG image may be displayed with misalignment or displayed with flickering, and therefore a synthesized image obtained by synthesizing together a captured image and a CG image may lack realness. Thus, it is not possible to sufficiently achieve the effect of “giving a feel as if the CG image actually existed”, which is the characteristic of augmented reality techniques.